1. Field of the Invention
The invention relates to torque machines for making and breaking screw-threaded joints between lengths of pipe. Such machines are commonly used in the oil industry for screwing together sections of drill pipe and the invention will be particularly described in relation to this application, although it will be appreciated that the invention is also applicable to torque machines for making and breaking screw-threaded pipe joints for other purposes.
2. Description of Related Art
The invention relates to torque machines of the kind including a rotatable head having an aperture which, in use, surrounds a length of the pipe to be joined, the rotatable head having mounted thereon a plurality of powered jaws which are spaced apart around the aperture and which are movable inwardly and outwardly towards and away from the length of pipe. The machine will normally also include a non-rotatable head and jaw assembly for holding one pipe section stationary while the other pipe section is rotated by the rotatable head. One pipe section is passed through the stationary head and the jaws of that head are moved inwardly so as to tightly grip the pipe section. The other pipe section is similarly introduced through the aperture in the rotatable head until its threaded end is in contact with the threaded end of the other pipe section and the jaws moved inwardly to grip the pipe. The rotatable head is then rotated so as to screw the pipe sections together to form the joint, the two heads being capable of axial movement towards and away from one another as the joint is made up or broken.
A disadvantage with existing torque machines of this type is that the maximum inward and outward travel of the jaws is comparatively small, for example of the order of half an inch, with the result that each head and jaw assembly is suitable for use with only one nominal diameter of pipe. For example, a head assembly with jaws suitable for use with 41/2" pipe cannot be used with 7" pipe. If it is required to change the size of pipe to be connected, it is necessary to replace the jaws with ones suitable for the new pipe size, and in some cases replacement of the whole head assembly may be necessary. This can be a time-consuming and laborious task.
Furthermore, when using some types of pipe, for example pipe with a high chromium content, it may be necessary or desirable to avoid marking the surface of the pipe by the jaws. With existing torque machines, this may be achieved by replacing the innermost part of each jaw by a so called "soft shoe", designed to grip the pipe without marking it. However, it is again a time-consuming and labourious operation to fit such shoes and to replace them when a new size of pipe is to be handled. Also, it is often found that presently available soft shoes may not be completely non-marking and although they may be an improvement on the standard jaw jaws they may still leave indentations on the pipe.
The present invention sets out to provide improved apparatus and methods for overcoming these disadvantages.